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"If you don't have to go out this morning, don't go," said Jeff Lindner, meteorologist with the Harris County Flood Control District.

There is not a lot of rain expected this morning, Lindner said, so the respite will give water levels a chance to recede.

Three to six inches of rain fell overnight in the central, western, and southern parts of the county, which includes Houston, with bayou and creek flooding and water on the streets. Some homes and businesses also were flooded, Lindner said.

More heavy rain later

While there was a lull in the heavy rain Friday morning, CNN meteorologist Gene Norman said, another round of battering storms was expected Friday night going into Saturday.

It would be another blow for the already rain-soaked region already.

"This has been a week-long slow-moving train wreck, where some people have seen more than a foot of rain," Norman said.

The intensity of the storm overnight brought out the first responders.

Rescuers raced to vehicles stuck in flooding on a major interstate Thursday night and to help other motorists trapped on other thoroughfares as slashing rain -- accompanied by hail and lightning -- deluged the region.

"Houston is no stranger to flooding, but it always seems to come at the worst time," Norman said, referring to storms during overnight hours.

In one instance, rescuers responded to a vehicle upside down and submerged in a flooded ditch and the occupant was "trapped but still alive," the Houston Fire Department tweeted.

Police tweeted that in the eastern section of the city, "barricades are up at two intersections to keep motorists from entering underpasses.

The Houston Police Department received reports of about 40 people trapped on East Interstate Highway 10 at Wayside by flood waters Thursday and sent a high-water rescue vehicle to the area, the department said.

Video shows vehicles stranded on the interstate, a portion of which was temporarily closed in both directions. The Houston Police Department said other roads in the area are still closed.

Houston Fire Department spokeswoman Sheldra Brigham tweeted images of the department taking emergency calls from all over the city late Thursday night.

Nearly half of all flash flood fatalities occur in vehicles, Brigham said on Twitter, and two feet of water can float most vehicles.

Flash flood watch

More than 20 million are under a flash flood watch through Saturday evening from southeastern Texas into most of Louisiana and Mississippi, CNN meterologist Dave Hennen said.

Water is reported to have reached some homes and businesses and at least four creeks and at least three bayous are presently overflowing, according to data from the Harris County Flood Warning System.

The high water has closed or delayed the start of the school day for 18 school districts in the area Friday, and there were more than 64,000 power outages in the early hours of the morning, according to CenterPoint Energy.

The power company says its crews will be working 16-hour shifts during the severe weather.

Rains trap students earlier in the week

This is the second time this week the heavy rainfall has been hazardous to those in southeast Texas.

About 60 students were stranded overnight Tuesday at a Cleveland, Texas, elementary school after downpours kept buses and parents off the roads, according to Cleveland Independent School District spokeswoman Susan Ard.

Another school district, New Caney Independent, posted on Twitter that it was also unable to transport students home after school, but remained open for parents to pick up their children.

Sugar Land, southwest of Houston, had more than 10 inches of rain, the National Weather Service said Wednesday.

There were 250 calls for high-water rescue to the Houston Fire Department, Brigham said on Twitter Tuesday, and that "hundreds of homes" had been affected by the rising waters.

CORRECTION: A previous version of this story incorrectly spelled the name of Jeff Lindner, meteorologist with the Harris County Flood Control District.